1. Field of the Invention
The present invention relates to a semiconductor device that has a semiconductor element typified by a transistor.
2. Description of the Related Art
In recent years, technology that is used to form thin film transistors using semiconductor thin films (with thicknesses of from several nanometers to several hundreds of nanometers, approximately) that are formed over substrates that have an insulating surface has been attracting attention. Instead of silicon wafers that are manufactured by thinly cutting an ingot of a single-crystal semiconductor, semiconductor substrates called silicon-on-insulator (SOI) substrates have been developed, which have a thin single crystalline semiconductor layer over an insulating film. Also, semiconductor devices in which the semiconductor substrate is used have been developed.
Semiconductor elements such as thin film transistors and MOS transistors are formed by stacking a conductive film, a semiconductor film, and an insulating film, and each film is formed by a sputtering method, a plasma CVD method, a coating method, or the like.
Film formation over a substrate in a plasma CVD apparatus has a problem in that reaction products are deposited in a reaction chamber, and when the deposited products are accumulated thick, the deposited products flake away on the substrate, which causes operation defects of a semiconductor element to be manufactured.
Thus, the inside of the reaction chamber is cleaned by the chemical reaction after film formation for a certain period. Specifically, the deposition products in the reaction chamber are removed using fluorine plasma or a cleaning liquid.
On the other hand, there is a problem in that a gas or liquid used for cleaning is left in the reaction chamber, and the residual gas or liquid is mixed into a film formed over the substrate. Therefore, there is an example in which a protective film is formed on an inner wall of the reaction chamber after the reaction chamber is cleaned (Reference 1: Japanese Patent No. 3400293).